1. Field of the Invention
The present invention relates to an automatic stop and start control system for an internal combustion engine mounted on a vehicle, which controls automatically stopping and restarting the engine, when the vehicle is stopped (an idle stop control for stopping unnecessary idling of the engine).
2. Description of the Related Art
A hybrid vehicle employs an internal combustion engine and an electric motor in combination. A conventional technique for idle stop control is known. When restarting the engine with the conventional technique, the motor is first operated to perform cranking and the engine is started at the time the engine rotational speed becomes a starting rotational speed (Japanese Patent Laid-open No. 2000-204997).
In the technique described in the above publication, the starting rotational speed is set to a value which decreases with an increase in the required drive force. Thus, when the required drive force increases, the engine is started earlier. Accordingly, when the driver of the vehicle depresses an accelerator pedal immediately after starting of the engine, the engine is restarted earlier.
But in some circumstances, it is preferable to perform engine restarting as quickly as possible irrespective of the magnitude of the required drive force to reduce the load on the motor in the hybrid vehicle. In the case of performing the idle stop control in a normal vehicle driven by only an internal combustion engine, the engine restarting must be performed as quickly as possible. For example, when the removal of a depression force applied to a brake pedal is detected, it may be determined that the driver intends to start the vehicle.
FIGS. 12A to 12E are time charts illustrating engine restart control in the prior art, which is directed to a four-cylinder internal combustion engine. FIG. 12A shows the strokes in the four cylinders (#1, #2, #3, and #4 cylinders). FIG. 12B shows an output from a brake switch for detecting the condition of a brake (the low level in FIG. 12B indicates the release of the brake). FIG. 12C shows TDC pulses generated immediately before the piston in each cylinder reaches a top dead center. FIGS. 12D and 12E respectively show drive control signals for fuel injection valves and ignition signals for four cylinders.
When the brake is released and a starter motor is operated to start cranking the engine, simultaneous injections of fuel into the four cylinders is carried out after generation of the first TDC pulse P11. At this time, the fuel is first introduced into the #4 cylinder on the intake stroke, and is next ignited by a spark generated by a spark plug for the #4 cylinder in the explosion (combustion) stroke after the compression stroke, thus generating the first explosion. When contemplating the #4 cylinder in which the first explosion is generated, this cylinder is on the exhaust stroke during stoppage of the engine, and shifts to the intake stroke after starting the cranking, via the compression stroke, to reach the explosion stroke. That is, about one and half revolutions of a crankshaft are required until the first explosion is generated after starting the cranking, and the first explosion is generated after the generation of three TDC pulses P11, P12, and P13.
FIG. 13 is a time chart showing changes in engine rotational speed and generation of TDC pulses, when actually starting the engine using the control method shown in FIGS. 12A to 12E. As understood from FIG. 13, the first explosion is generated after generating three TDC pulses after starting the cranking.
It is preferable, however, to restart the engine after the idle stop as quickly as possible. Thus, further improvement is desired.
It is accordingly an object of the present invention to provide an automatic stop and start control system for an internal combustion engine, which can restart the engine quicker than the prior art.
To attain the above object, the present invention provides an automatic stop and start control system for a multiple-cylinder internal combustion engine mounted on a vehicle. The control system controls automatically stopping and restarting the engine according to operating conditions of the vehicle and the engine. The control system includes fuel supply stop control means and fuel supply start control means. The fuel supply stop control means provides fuel to at least one of the cylinders of the engine when an engine stop condition for stopping the engine is satisfied. And then stops the fuel supply to all of the cylinders of the engine. The fuel supply start control means immediately supplies fuel to at least one of the cylinders at the time an engine restart condition for restarting the engine is satisfied.
With this configuration, the fuel supply is provided to at least one of the cylinders of the engine when the engine stop condition is satisfied, and subsequently the fuel supply to all of the cylinders of the engine is stopped. Thereafter, at the time the engine restart condition is satisfied, fuel is immediately supplied to at least one of the cylinders of the engine. By providing the fuel supply to at least one cylinder upon stoppage of the engine, the combustion (first explosion) is carried out by the first ignition pulse upon restart of the engine, and by supplying fuel at the beginning of restart of the engine, the combustion by the second ignition pulse is subsequently carried out. Accordingly, the first explosion can be generated earlier and the engine restarted quicker than in the prior art.
Preferably, when the engine stop condition is satisfied, the fuel supply stop control means first stops the fuel supply to a first predetermined number of cylinders and then provides fuel to at least one cylinder.
In the above configuration, xe2x80x9cthe first predetermined numberxe2x80x9d is set so that the at least one cylinder to which the fuel is supplied stops in the compression stroke when the engine is stopped. Specifically, the first predetermined number is set to xe2x80x9c2xe2x80x9d for a four-cylinder engine. This number is also set to xe2x80x9c2xe2x80x9d for six-cylinder or eight-cylinder engines. That is, the first predetermined number is set to a fixed value regardless of the number of cylinders.
With this configuration, the fuel supply to the first predetermined number of cylinders is first stopped when the engine stop condition is satisfied. Then the fuel supply is provided to the at least one cylinder. Accordingly, the engine can be reliably stopped, and the emission of unburnt fuel can be prevented.
Preferably, the control system further includes ignition control means for first carrying out ignitions of a second predetermined number of cylinders when the engine stop condition is satisfied, and then suspending the subsequent ignition.
In the above configuration, xe2x80x9cthe second predetermined numberxe2x80x9d is set to the number of such cylinders that the fuel is supplied before the engine stop condition is satisfied and the ignition timing comes after the engine stop condition is satisfied. Specifically, the second predetermined number is set to xe2x80x9c2xe2x80x9d for a four-cylinder engine, xe2x80x9c3xe2x80x9d for a six-cylinder engine, and xe2x80x9c4xe2x80x9d for an eight-cylinder engine.
With this configuration, the ignition to the second predetermined number of cylinders is carried out when the engine stop condition is satisfied, and the subsequent ignition is suspended. Accordingly, the fuel supplied before the engine stop condition is satisfied, can be reliably burned, and unnecessary ignitions after the engine stop condition is satisfied, can be prevented.
Preferably, the vehicle has a motor capable of rotationally driving an output shaft of the engine and performing a regenerative operation for converting rotational energy of the output shaft into electrical energy. The control system further includes regeneration control means for performing the regenerative operation of the motor when the engine stop condition is satisfied.
With this configuration, the regenerative operation of the motor is performed when the engine stop condition is satisfied. Accordingly, the engine can be stopped earlier by a braking effect due to the regenerative operation.
Preferably, the fuel supply start control means includes fuel amount control means for decreasing a fuel amount to be supplied to the engine as compared with the fuel amount in normal control, during a first predetermined time period from the time the engine restart condition is satisfied.
With this configuration, the fuel amount to be supplied to the engine is decreased as compared with that in normal control during the first predetermined time period from the time the engine restart condition is satisfied. Accordingly, the air-fuel ratio of an air-fuel mixture to be supplied to the at least one cylinder is controlled to be leaner than that in normal control. Thus, self-ignition can be reliably prevented, and the air-fuel mixture supplied can be reliably ignited upon restarting the engine.
Preferably, the control system further includes retard control means for retarding an ignition timing of the engine from the ignition timing in normal control, during a second predetermined time period from the time a rotational speed of the engine equals or exceeds a predetermined rotational speed when restarting the engine.
With this configuration, the ignition timing of the engine is retarded from that in normal control during the second predetermined time period from the time the rotational speed of the engine equals or exceeds the predetermined rotational speed when restarting the engine. Accordingly, the output from the engine can be suppressed to thereby prevent a rapid increase in the engine rotational speed.
Preferably, the engine is provided with intake air amount increasing means for increasing an intake air amount to the engine. The control system further includes air-fuel ratio adjusting means for increasing the intake air amount by operating the intake air amount increasing means after the engine stop condition is satisfied.
With this configuration, the intake air amount is increased by the intake air amount increasing means after the engine stop condition is satisfied. Accordingly, the air-fuel ratio of an air-fuel mixture to be supplied to the at least one cylinder is controlled to be leaner than that in normal control. Thus, self-ignition can be reliably prevented, and the air-fuel mixture supplied can be reliably ignited upon restarting the engine.
More preferably, the control system further includes inhibiting means for inhibiting an operation of the intake air amount increasing means during a third predetermined time period from the time the engine restart condition is satisfied.
With this configuration, the operation of the intake air amount increasing means is inhibited during the third predetermined time period from the time the engine restart condition is satisfied, so that the intake air amount is not increased. Accordingly, the engine output can be suppressed to thereby prevent a rapid increase in the engine rotational speed.